全文获取类型
收费全文 | 5028篇 |
免费 | 121篇 |
国内免费 | 24篇 |
专业分类
化学 | 3214篇 |
晶体学 | 25篇 |
力学 | 165篇 |
数学 | 736篇 |
物理学 | 1033篇 |
出版年
2023年 | 31篇 |
2022年 | 104篇 |
2021年 | 125篇 |
2020年 | 74篇 |
2019年 | 97篇 |
2018年 | 63篇 |
2017年 | 75篇 |
2016年 | 193篇 |
2015年 | 115篇 |
2014年 | 160篇 |
2013年 | 263篇 |
2012年 | 306篇 |
2011年 | 361篇 |
2010年 | 219篇 |
2009年 | 214篇 |
2008年 | 306篇 |
2007年 | 320篇 |
2006年 | 258篇 |
2005年 | 266篇 |
2004年 | 222篇 |
2003年 | 202篇 |
2002年 | 168篇 |
2001年 | 61篇 |
2000年 | 76篇 |
1999年 | 50篇 |
1998年 | 46篇 |
1997年 | 51篇 |
1996年 | 71篇 |
1995年 | 57篇 |
1994年 | 56篇 |
1993年 | 34篇 |
1992年 | 26篇 |
1991年 | 29篇 |
1990年 | 32篇 |
1989年 | 41篇 |
1988年 | 27篇 |
1987年 | 25篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 44篇 |
1983年 | 19篇 |
1982年 | 29篇 |
1981年 | 34篇 |
1980年 | 28篇 |
1979年 | 20篇 |
1978年 | 22篇 |
1977年 | 13篇 |
1975年 | 13篇 |
1974年 | 10篇 |
1970年 | 8篇 |
排序方式: 共有5173条查询结果,搜索用时 15 毫秒
11.
We review the proof of a conjecture concerning the reality of the spectra of certain PT-symmetric quantum mechanical systems, obtained via a connection between the theories of ordinary differential equations and integrable models. Spectral equivalences inspired by the correspondence are also discussed. 相似文献
12.
Roberto Raucci 《Rendiconti del Circolo Matematico di Palermo》1998,47(1):113-128
In this paper a two level optimization problem, in which the problem of inferior level is a Nash-problem with general constraints
(rappresented by multifunctions) and with a unique solution, is considered. On the problem of inferior level approximation
results of the solution are proved, on the problem of superior level existence and approximation results of the solutions
are proved.
相似文献
13.
Jos Vargas Carlos Ramos Roberto D. Zysler Hctor Romero 《Physica B: Condensed Matter》2002,320(1-4):178-180
Chemically prepared (CoxNi1−x)1−yBy (x=0.5, 0.75, 1; y≈0.4) amorphous fine particles were characterized by X-ray diffraction, DTA and TGA, and in situ magnetic measurement as a function of annealing temperature in an inert atmosphere. Magnetic measurement performed in as-prepared and 150°C annealed samples shows an increase of the saturation magnetization and magnetic moment after thermal treatment. Room temperature magnetization increases by factors of 3.5, 1.8, and 1.5, for x=0.5, 0.75, and 1, respectively. These measurements may indicate a local re-ordering of the amorphous phase at temperatures much lower than the full crystallization temperature. 相似文献
14.
We investigate decay properties of correlation functions in a class of chaotic billiards. First we consider the statistics of Poincaré recurrences (induced by a partition of the billiard): the results are in agreement with theoretical bounds by Bunimovich, Sinai, and Bleher, and are consistent with a purely exponential decay of correlations out of marginality. We then turn to the analysis of the velocity-velocity correlation function: except for intermittent situations, the decay is purely exponential, and the decay rates scale in a simple way with the (uniform) curvature of the dispersing arcs. A power-law decay is instead observed when the system is equivalent to an infinite-horizon Lorentz gas. Comments are given on the behaviour of other types of correlation functions, whose decay, during the observed time scale, appears slower than exponential. 相似文献
15.
Roberto H. Schonmann 《Communications in Mathematical Physics》1989,124(1):1-7
Consider the + phase of the two dimensional nearest neighbor ferromagnetic Ising model at a temperature belowT
c
. Let + be the restriction of this measure to a coordinate axis. We prove that there is no one dimensional translation invariant summable interaction for which + is a Gibbs measure. This is proven by showing that if such an interaction existed, + would have large deviation properties different from those it actually has. Percolation methods are used in the proof.Work supported by the U.S. Army Research Office through the Mathematical Sciences Institute at Cornell and by a NSF grant to Cornell. This work was finished while the author was visiting Rutgers University, being supported by the NSF grant 86-12369 相似文献
16.
Substrate relaxation is shown to play an important role in the 1 : 2 regular chemisorption of hydrogen atoms above alternate carbon atoms in a graphite monolayer. Binding energy, population analysis and electron density maps show that the direct HC bond is strengthened on relaxation. 相似文献
17.
Nelson Durán Klaus Zinner Roberto Casadei de Baptista Carmen C. C. Vidigal Giuseppe Cilento 《Photochemistry and photobiology》1976,24(4):383-388
Abstract— The thiophenyl ester of indole-3-acetic acid and indole-3-acetonitrile produce chemiluminescence in aerated dimethylsulfoxide in the presence of potassium t -butoxide. The emitter is the aromatic aldehyde. In the case of acetonitrile, the other product expected from the cleavage of an intermediate dioxetane, cyanate/isocyanate, has also been identified. Other auxins also chemiluminesce under similar conditions, but the emitters have not been properly identified.
These systems are models for the peroxidase catalyzed oxidation of indole-3-acetic acid to indole-3-carboxaldehyde and as such support the earlier inference (Vidigal et al , 1975) that the excited aldehyde is generated in the enzymic process.
An additional result is the observation of an exciplex between excited indole-3-carboxaldehyde and the thiophenylester of indole-3-acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route. 相似文献
These systems are models for the peroxidase catalyzed oxidation of indole-3-acetic acid to indole-3-carboxaldehyde and as such support the earlier inference (Vidigal et al , 1975) that the excited aldehyde is generated in the enzymic process.
An additional result is the observation of an exciplex between excited indole-3-carboxaldehyde and the thiophenylester of indole-3-acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route. 相似文献
18.
Apparent molal heat capacities
of some piperidine, morpholine, and piperazine derivatives in aqueous solution have been determined by adiabatic calorimetry
in the temperature range 20–55°C and in the molality range 0.2–1m. Comparison of experimental
values with those calculated through group contributions, found for monofunctional compounds, indicates strong interactions
between the hydrophilic centers. An interpretation is given of the possible mechanism of this interaction. Also, values of
ΔC
p
for the addition reaction of proton to nitrogen centers of mono- and bifunctional organic compounds are examined. 相似文献
19.
20.
Aringhieri Roberto Bigharaz Sara Duma Davide Guastalla Alberto 《Central European Journal of Operations Research》2022,30(1):189-211
Central European Journal of Operations Research - Disaster management generally includes the post-disaster stage, which consists of the actions taken in response to the disaster damages. These... 相似文献